The present invention relates to a rear-projection image display. More specifically, the present invention relates to a rear-projection image display in which image display is conducted by superimposing projection images on a transparent screen, the projection images being projected from a plurality of image displays juxtaposed in a common horizontal plane.
The following description will depict a conventional rear-projection image display, while referring to the drawings.
FIG. 7 is a plan view illustrating an overall configuration of a conventional three-tube rear-projection image display 100. The rear-projection image display (video projector) 100 presently is a main item in the market of large video-image display for home use. Images on three image display elements (CRTs) 101, 102, and 103 corresponding to three colors of red, green and blue colors, respectively, are enlarged and projected by projection lenses 104, 105, and 106, respectively, so as to be synthesized on a transparent screen. The transparent screen includes a Fresnel lens 107 as collimating means and a lenticular lens sheet 108 as a light diffusing means. Such a transparent screen can collimate respective principal rays of color lights incident from different directions and then allows the same to leave. Hence, a phenomenon can be corrected in which shade of color varies with positions where the observer stands (color shading). In addition, on a light-outgoing surface of the lenticular lens sheet 108, black stripes 109 are provided between adjacent lenticular lenses so as to prevent black dimming from occurring due to external light, and thus to prevent lowering of the contrast of images. Furthermore, surfaces of the lenticular lenses between the black stripes 109 are coated with a diffusing material, or a diffusing material is mixed in the lenticular lens sheet 108, so that visibility is secured in a vertical direction.
On the foregoing transparent screen, however, light source images of three different color lights are formed at different positions within an aperture between adjacent black stripes 109, as illustrated in FIG. 8. Therefore, in order to avoid optical loss, it is necessary to make each space between the black stripes 109 sufficiently wide with respect to the foregoing light source images. This causes the black stripes 109 to be sparsely provided. Consequently, it has been impossible to suppress sufficiently the black dimming caused by the diffusing material reflecting external light that has entered through the aperture.
Screens that solve such a problem recently have been proposed, which are as described below. Such screens include: a first type of screen disclosed in JP 9(1997)-504882 A in which transparent beads are used; a second type of screen is disclosed in JP 10(1998)-339915 A in which black stripes are used; and a third type of screen is disclosed in the JP 10(1998)-111537 A in which a color layer is used.
A configuration of a transparent screen of the first type using transparent beads is shown in FIG. 9. Micro beads 111 made of a transparent material are fixed to a substrate panel 110 made of a light-transmitting material with a light absorbing adhesive 112 used therebetween. Light having passed through the Fresnel lens 107 is converged by the beads 111 so as to be focused on portions (apertures) where the beads 111 and the substrate panel 110 are in contact with each other. Since the adhesive 112 is absent at these portions, the light passes through the substrate panel 110 to leave as diffused light. Each of the portions (apertures) where the beads 111 and the substrate panel 110 are in contact with each other is a very small point that occupies an area that hardly can be recognized when viewed from the observer side, and areas of the screen surface other than the apertures are covered with the light absorbing adhesive. Most of external light incident on the screen from the surroundings therefore is incident on and absorbed by the adhesive, never to be reflected toward the observer side. In this screen, such very small beads 111 allow high-definition display to be provided. Besides, the black level hardly is impaired even when strong external light is incident on the screen. Consequently, the contrast of images hardly is impaired.
A configuration of a transparent screen of the second type using black stripes is shown in FIG. 10. A lenticular lens sheet 113 includes lenticular lenses on a light-incident surface thereof, and a diffusing layer 116 is laminated on a light-outgoing surface of the lenticular lens sheet 113. Black stripes 115 are formed on a light-outgoing surface of the diffusing layer 116, and the diffusing layer 116 is laminated with a front panel 114 with a transparent adhesive layer being provided therebetween. Light having passed through a Fresnel lens 107 enters the lenticular lenses, is converged onto apertures between the black stripes 115 or the vicinities thereof, passes through the front panel 114, and exits as diffused light. In the foregoing process, when passing through the diffusing layer 116, image light is diffused in horizontal and vertical directions. Since the lenticular lenses that are very small are used to converge the image light, it is possible to narrow the spaces between the black stripes 115. This allows a proportion of areas of the black stripes 115 to be increased, thereby causing most of the external light incident on the screen to be absorbed by the black stripes 115, never to be reflected toward the observer side. This configuration of the screen therefore allows the lenticular sheet 113 to be formed thinly, thereby allowing the black stripes 115 to be provided at a fine pitch. Consequently, a high-definition display can be provided. Besides, the black level hardly is impaired even when strong external light is incident on the screen. This results in that the contrast of images hardly is impaired.
A configuration of a transparent screen of the third type using a color layer is shown in FIG. 11. A lenticular lens sheet 118 includes lenticular lenses 117 on a light-incident surface thereof, and a color layer 119 is provided in the vicinity of the light-incident surface of the lenticular lenses 117. A material of the lenticular lens sheet 118 as a substrate is either non-colored, or colored to have a lighter tint than that of the color layer 119. Light having passed through a Fresnel lens 107 enters the color layer 119. After passing through the color layer 119, the light enters the lenticular lenses 117. The light is converged by the lenticular lenses 117 and is allowed to exit as diffused light to the observer side.
On the other hand, among external light from the surroundings, light incident to the color layer 119 at a small angle of incidence passes through the color layer 119 and is absorbed into a case, with substantially no light going back to the screen. Therefore, the light incident to the layer 119 at a small angle of incidence is not harmful. Moreover, light incident on the color layer 119 at a great angle of incidence is subjected to total reflection at an interface between the color layer 119 and an air layer. Normally the total reflection is repeated several times, and then some light follows an optical path going back to the observer side However, since a distance for passage through the color layer 119 increases as the total reflection is repeated, most of the light therefore is absorbed by the color layer 119. Thus, this screen allows the lenticular lens sheet 118 to be formed thinly, thereby allowing the lenticular lenses 117 to be provided at a fine pitch. Consequently, a high definition display call be provided. Moreover, since the foregoing screen hardly allows external light incident on the screen to be reflected to the observer side without remarkable degradation of image light, incidence of strong external light onto the screen hardly causes the black level to lower, hence hardly causing the contrast of images to deteriorate.
In either of the foregoing screen using transparent beads or that using the black stripes, however, it is required to converge image light to the apertures each having a very small area by means of the light-incident-side lenses (the beads in the bead-using type, or the lenticular lenses in the black-stripe-using type). No problem occurs in the case where the screen is used in a display in which an image on the image display element for displaying color images is enlarged and projected by means of one projection lens. However, the following problem occurs in the case where the screen is used in a currently predominant projector in which images of the three CRTs are enlarged and projected by three projection lenses, respectively, to be superimposed on the screen, as shown in FIG. 7. Namely, since respective color lights are incident at different angles on the light-incident-side lenses, positions where the color lights are converged are different from one another. Accordingly, when the apertures are formed to be smaller, the color lights from the CRTs other than that positioned at the center are converged on a light absorbing layer, thereby resulting in a considerable decrease in light utilization efficiency and coloration out of balance.
Furthermore, when the screen with the color layer is used in the aforementioned projector in which images of three CRTs are enlarged and projected by three projection lenses, respectively, to be superimposed on one another on the screen, color lights of image light are incident on the light-incident-side lenses (lenticular lenses) at different angles of incidence, respectively. Accordingly, the respective color lights have different outgoing light intensity distributions, and this causes significant color shading.
As described above, the conventionally-proposed transparent screen does not have a drawback when being used as a screen in an image display in which a color image is enlarged and projected by means of one projection lens, but causes the following problem when being used as a screen in a currently predominant projector in which color images are superimposed on the screen using three CRTs and three projection lenses for respective colors. Namely, the respective color lights are incident on the light-incident-side lenses at different angles. Therefore, color lights from the CRTs other than the CRT positioned at the center are converged to the light absorbing layer, and this results in a drastic decrease in the light utilization efficiency and distortion of color balance. Furthermore, color shading, etc. also occurs.
An object of the present invention is to provide a rear-projection image display provided with three sets of image display elements and illuminating lenses for color lights, respectively. The rear-projection image display overcomes the aforementioned problems that tend to occur when the conventional transparent screen is used, and avoids the black dimming and the lowering of contrast due to entrance of external light.
To achieve the foregoing object, the present invention employs the following configuration.
A rear-projection image display of the present invention includes a trichromatic image projecting section, and a transparent screen on which images formed with respective color lights projected by the trichromatic image projecting section are superimposed to be displayed.
The foregoing trichromatic image projecting section includes three image projecting sections corresponding to colors of red, green and blue, respectively, the three image projecting sections being arrayed in one horizontal plane, each of the three image projecting sections including an image display element for displaying an image according to an input signal, and an illuminating lens for enlarging and projecting the image displayed by the image displays element.
The transparent screen includes, in an order from a side of the trichromatic image projecting section, a collimating means, a color-shading eliminating means, and a light diffusing means.
The foregoing collimating means converts incident light having a predetermined flare angle from each of the image projecting sections into telecentric light and allows the telecentric light to leave therefrom;
The foregoing color-shading eliminating means has, on its light-incident surface, light-incident-side lenticular lenses for converging incident light from the collimating means in a horizontal plane, and on its light-outgoing surface, light-exit-side lenticular lenses having one-to-one correspondence to the light-incident-side lenticular lenses, so as to allow principal rays of the respective lights of the colors to be substantially parallel with one another and to exit, the respective lights being from the image projecting sections and having passed through the collimating means.
According to a first configuration of the foregoing light diffusing means, the light diffusing means includes a substrate sheet, made of a transparent material and a plurality of micro beads made of a transparent material provided on the light-incident surface of the substrate sheet, light transmitting portions are formed between the substrate sheet and the micro beads, and the light-incident surface of the substrate sheet except for the light transmitting portions are covered with an opaque binder.
According to a second configuration of the light diffusing means, the light diffusing means includes, on its light-incident surface lenticular lenses that converge incident light from the color-shading eliminating means in a horizontal plane, black stripes formed with a material having a light absorbing property in a region except for places where the incident light is converged and vicinities thereof, and a light diffusing layer made of a material containing a light diffusing material.
According to a third configuration of the light diffusing means, the light diffusing means includes a substrate having, on its light-incident surface, lenticular lenses for converging incident light from the color-shading eliminating means in a horizontal plane, and a color layer formed at least in vicinities of light-incident surfaces of the lenticular lenses, a material of the substrate being non-colored, or colored to have a tint lighter than that of the color layer.
In the above-described rear-projection image display of the present invention, principal rays of the respective color lights that are incident at different angles are converted into substantially parallel rays by the color-shading eliminating means, and thereafter they are made to enter the light diffusing means that hardly is affected by external light. It is therefore possible to provide a projector (for instance, a three-CRT-type projector) equipped with a plurality of image projecting sections, in which display images hardly are affected by external light, an increased angle of visibility is provided, and less color shading is caused without a decrease in the light utilization efficiency.
The collimating means preferably is a Fresnel lens sheet and its focal length is substantially equal to a distance from the collimating means to each of the three image projecting sections. This preferable configuration allows the collimating means for obtaining telecentric light to be formed thinner and smaller in size.
The light-exit-side lenticular lenses of the color-shading eliminating means preferably are placed substantially at positions where the light-incident-side lenticular lenses form images, respectively. Besides, a focal length of each of the light-exit-side lenticular lenses of the color-shading eliminating means is substantially equal to a distance therefrom to a corresponding one of the light-incident-side lenticular lenses. This preferable configuration allows principal rays of the respective color lights that are incident at different angles of incidence to outgo in a substantially parallel state, and also allows the respective color lights that are incident in a substantially parallel state to be converged efficiently.
Each of the light-exit-side lenticular lenses of the color-shading eliminating means preferably has a width in a horizontal direction, the width covering an area where an image of the trichromatic image projecting section is formed by each of the light-incident-side lenticular lenses corresponding to each of the light-exit-side lenticular lenses. This preferable configuration enables to avoid both stray light and reduction of light utilization efficiency.
A width in a horizontal direction of the light-exit-side lenticular lenses of the color-shading eliminating means preferably is narrower than a width in the horizontal direction of the light-incident-side lenticular lenses, and a light absorbing agent is applied to spaces between any adjacent two of the light-exit-side lenticular lenses. This preferable configuration further enables securely avoiding stray light.
The color-shading eliminating means preferably is a lenticular lens sheet provided with the light-incident-side lenticular lenses on one surface thereof, and the light-exit-side lenticular lenses on the other surface thereof. By integrally providing the light-incident-side lenticular lenses and the light-exit-side lenticular lenses, the color-shading eliminating means can be formed smaller and thinner in size, and cost reduction call be achieved as well.